The present invention relates to a rolling mill with small diameter work rolls and, more particularly, to a cluster type rolling mill and a rolling method using the rolling mill.
Rolling mills provided with small diameter work rolls for the purpose of stably rolling a thin plate of hard material which is difficult to roll and a that requires high surface quality, are known for example, 20-stage Sendzimir mills, 10-stage cluster mills and 6-high rolling mills. Those types of rolling mills will be explained below.
(1) 20-stage Sendzimir Mill
The 20-stage Sendzimir mill is an original type of cluster mill which employs small diameter work rolls. The Sendzimir mill is disclosed in JP A 4-127901, for example.
The Sendzimir mill has, upper and lower work rolls each supported by nine rolls in total composed of two first intermediate rolls, three second intermediate rolls and four backing rolls. The first intermediate rolls each are tapering in shape at an axial end portion and each is shiftable in an axial direction by an axial shifting mechanism. The backing rolls each are divided into a plurality of roll sections in the axial direction (in the plate width direction) and a bearing position of each roll section is adjustable in the pass direction (which is a so-called AS-U backing roll mechanism).
Since the work rolls are small in diameter, the strength is insufficient for transmitting necessary rolling torque through twisting of the work roll. The torque necessary for rolling is transmitted, as tangential force, from the intermediate rolls as driving rolls to the work rolls. In each work roll, horizontal deflection is caused by the tangential force and a rolling load, which becomes the cause of defective shape of a rolling plate.
Therefore, in the rolling mill, the deflection is suppressed to effect excellent shape control by three means of mainly 1) axial shift of the first intermediate roll, 2)crown control of the backing rolls by the AS-U backing roll mechanism, and 3) cluster type support of each work roll by two intermediate rolls.
(2) 10-stage Cluster Type Rolling Mill
An example of a conventional 10-stage cluster type rolling mill is disclosed in JP A 58-50105, for example.
This rolling mill has upper and lower work rolls each supported by four rolls in total composed of two intermediate rolls and two backing rolls. The two backing rolls each are divided into a plurality of roll sections in the axial direction (in the plate thickness direction) as in the 20-stage Sendzimir rolling mill (1), and provided with an AS-U backing roll mechanism. Further, the backing rolls, the intermediate rolls and the work rolls each are supported by chocks, each of which is movable in the housing in the up and down directions. The chocks for the intermediate rolls and work rolls of those chocks are provided with actuators for imparting bending force.
In this types of rolling mill, deflection of the work rolls as mentioned above is suppressed to effect excellent shape control by three means of mainly 1) bending of the work rolls and the intermediate rolls, 2)crown control of the backing rolls by the AS-U backing roll mechanism, and 3) cluster type support of each work roll by the two intermediate rolls.
(3) 6-high Rolling Mill
An example of a conventional 6-high rolling mills is disclosed in JP A 5-50109 and the The Hitachi Hyoron vol.78 No.6 pages 17-20 (1996.6), for example.
The 6-high rolling mill has upper and lower work rolls each supported by two rolls composed of only one intermediate roll and one backing roll. The backing roll, intermediate roll and work roll each are supported by chocks each of which is movable in the housing in the up and down directions as in the rolling mills (1) and (2), and actuators are provided for applying horizontal force on the chocks provided at the roll ends of the work roll.
Further, differing from the above-mentioned rolling mills (1) and (2), the backing roll is not axially divided but a one piece roll, and the work roll is able to be offset to the intermediate roll by moving a support roll supporting the work roll in the pass direction. Further, although not disclosed particularly in the above-mentioned prior art, a construction, other than this construction, in which an intermediate roll having a tapering shape in the axial end portion is made shiftable in the axial direction as in the above-mentioned rolling mill (1), has been already proposed.
In this rolling mill, as for the above-mentioned work roll horizontal deflection, the horizontal deflection of the work roll is suppressed to be small by balancing the offset component of a rolling load caused by offsetting the work roll from the intermediate roll with the roll driving tangential force, and cancelling at the same time the horizontal deflection due to horizontal bending of the work roll and the horizontal deflection due to the tangential force from the intermediate roll and a variation component of the rolling material tension.
However, the above-mentioned prior art still have the following problems.
First since the 20-stage Sendzimir rolling mill has a construction such that all the rolls are covered with the upper and lower housings, it is impossible to provide a mechanism for imparting bending force to the work rolls and the intermediate rolls. Therefore, it is difficult to obtain products such as fine steel materials which are thin and wide and required of high shape precision. Further, because of such a construction, a large gap can not be made between the upper and lower work rolls, so that the facility of passing of a plate is bad and it is impossible to directly detect the rolling load. Further, since the rolling load can not be directly detected, thickness control becomes complicated. Further, marks of the backing roll sections formed by division of a roll in the axial direction are finally transferred to and left on the plate surface through the third intermediate rolls and the second intermediate rolls, so that there is left the problem that the surface quality is lost.
On the other hand, the 10-stage cluster type rolling mill can impart bending force to the work rolls and the intermediate rolls, so that it is possible to easily satisfy the severe requirement of shape precision. Since the backing rolls, intermediate rolls and work rolls are supported by the chocks which are movable in the housing in the up and down directions, it is possible to secure a roll gap at the time of plate passage and to directly detect the rolling load.
However, there is still a the problem that the surface quality becomes bad due to marks of the divided roll sections left on the surface as well as in the above-mentioned 20-stage Sendzimir rolling mill. In particular, in the case of this 10-stage cluster rolling mill, the second intermediate rolls as used in the Sendzimir rolling mill are omitted in order to raise a shape control effect by the division type backing rolls. In such a construction, only one intermediate roll between the work roll and each backing bearing exists, so that marks of the divided backing roll sections are easier to be transferred than in the 20-stage Sendzimir rolling mill and the rolling mill is difficult to be applied for rolling materials required of high surface quality.
In the 6-high rolling mill, the backing roll is a one-piece roll, so marks are not transferred onto the plate and the surface quality of products is not lost, differing from the case of the division type backing rolls. Further, it is possible to easily satisfy the severe requirement of the surface quality by variable offset control and horizontal bending of the work rolls. Further, since the backing rolls, intermediate rolls and work rolls are supported by the chocks which are able to move in the housing in the up and down directions, it is possible to secure a roll gap at the time of passage of a plate and to directly detect a rolling load.
However, although the variable offset control and horizontal bending control bring out their excellent performance in the case where a rolling torque is small relative to a rolling load and in the case of one-way rolling, there is left the problem that control pattern at operation becomes very complicated and the productivity decreases in the case where contact force direction changes reversely each pass of the rolling material as in a reversing rolling mill and in the case where the rolling torque changes largely compared with the rolling load.
An object of the present invention is to provide a cluster type rolling mill and rolling method which can execute excellent shape control by controlling deflection of the work rolls without worsening the surface quality of plate materials, prevent the production efficiency from lowering even if the rolling torque largely changes, and secure good plate passage facility and directly detect a rolling load.